1. Field of the Invention
The present invention relates to a directional rotary drilling method and apparatus; specifically, to a method and apparatus for moving a drill bit along a desired path.
2. Related Art
All methods known to applicant use some manner of mechanical contact with the well bore to achieve the desired steering of the drilling tool, or as in the case of point-the-bit methods, the steering is achieved by offsetting the angle of the drill bit axis relative to the rest of the drill tool. Fluid pressure necessary to cause fluid flow through changing flow geometries (orifices, bends, narrow passages, conduits, etc.) commonly described as pressure loss is typically considered a negative effect of changing flow conditions because it often requires alternative design requirements. That same changing fluid flow conditions is used in the described method and apparatus to create a pressure differential between the two sides of the drilling tool and thereby achieve a desired lateral force on the drilling tool useable for steering the tool in the given direction. There have been attempts to use changing directional fluid flows that are different than this invention and not intended to use the hydraulic pressure difference around the drilling tool for steering the tool in the preferred direction. See U.S. Pat. No. 4,836,301 as an example of these types of fluid directing systems, which uses changing direction of drilling fluid flow inside the drilling tool to generate a hydrodynamic force to tilt the drill bit axis in a given direction using a point-the-bit steering method and system.